Field of the Invention
The invention relates to a sheet transport system, a propulsive drive device, a web infeed device and a transport gripper system for a rotary printing machine including a sheet transport device having a sheet holder, and a first and a second propulsive drive element for propulsively driving the sheet transport device guidingly in a first and a second guide rail, respectively, the second guide rail extending substantially parallel to the first guide rail, the first and the second propulsive drive elements forming rotors of an electric linear drive, the first and the second guide rails having a plurality of drive stations disposed thereon and forming a stator of the linear drive, and a control device assigned to the drive stations for controlling and regulating movement of the first and the second propulsive drive elements. Sheet transport systems for rotary printing presses have become known heretofore in the prior art and are installed or used, for example, in the feeder region of a printing press to remove a sheet from a sheet pile and to feed the sheet to a first printing unit. Furthermore, it has become known heretofore to use sheet transport systems for transporting sheets within the printing press from printing unit to printing unit or for transporting the sheets from the last printing unit to a delivery pile in a delivery region, the transport of the sheets in the different printing press sections being generally performed by variously constructed sheet transport systems. Thus, in the feeder region, mechanically driven, mainly rectilinearly displaced suction devices in the form of lifting and dragging suckers are used. Between the printing units, i.e., within the printing press, the sheet transport is then usually performed by sheet transfer cylinders or drums with gripper devices arranged thereon. In the delivery region, the sheets are finally transported by gripper bars, which are fixed to two revolving endless chains arranged parallel to one another.
Furthermore, the German Non-prosecuted Patent Application (DE-OS) 25 01 963 discloses the practice of transporting the sheets through the entire printing press with the aid of a sheet transport system in the form of a gripper carriage with a gripper bar arranged thereon. The gripper carriage is driven, in this regard, by first and second propulsive or forward drive elements, which are guided in appertaining endless guide rails running at both sides in the housing of the printing press, and form the rotor of an electric linear motor. Extending along the two guide rails are endless stator coils, which produce an electromagnetic traveling field for the propulsive drive of the gripper carriage. In this regard, provision may be made for the coils to be subdivided into a plurality of electrically independent subsections, which are assigned to the respective printing units, in order to be able to control the speed of the gripper carriage with high accuracy, for example, when it is passing a press nip. A disadvantage of the aforedescribed sheet transport system is that the stator coils are constructed as endless coils, which leads to a high electrical power demand and makes necessary a comparatively high control and regulation outlay and the corresponding costs associated therewith. Thus, particularly in order to achieve the in-register feeding of sheets into the press nips of the respective printing units, it is necessary to drive each individual winding of the endless coil by a separate control device, in order to attain the required accuracy.